The importance of sputter-coated glass layer systems for achieving solar management properties in many types of glass articles, such as architectural windows and doors, is now well established in commerce. In addition, the importance of using such layer systems in insulating glass units (known as "IG" units in the art) is equally well established. Examples of this latter use include multipaned windows and doors made up of at least two panes of glass sealed at their peripheral edges to form an insulating chamber therebetween. Such chambers, in this respect, are often made by evacuating the air from the chamber, heat sealing the glass panes at their edges and filling the chamber formed with a gas other than air, such as argon.
Important to the acceptance of solar management glasses, including IG units, in the marketplace are the following characteristics which relate directly to the sputter-coated layer system employed:
1) the desired amount of visible transmittance coupled with an acceptable level of infrared radiation reflectance; PA1 2) a non-mirror-like appearance (i.e. a low visible "reflectance" as defined below); PA1 3) a substantially neutral visible reflected color when viewed from the glass side (i.e. a color falling within the range of from colorless to slightly blue); PA1 4) resistance to weathering or other chemical attack, often referred to as "chemical durability" (this term is defined below); and PA1 5) resistance to abrasion (often referred to as "mechanical durability", a term also defined below) during handling, particularly during the various steps necessary to produce an IG window or door from two or more sheets of glass, at least one of which has been pre-sputter-coated with the aforesaid layer system. PA1 a) an undercoat layer of Si.sub.3 N.sub.4 ; PA1 b) a layer of nickel or nichrome; PA1 c) a layer of silver; PA1 d) a layer of nickel or nichrome; and PA1 e) an overcoat layer of Si.sub.3 N.sub.4. PA1 glass/Si.sub.3 N.sub.4 /Ni:Cr/Ag/Ni:Cr/Ag/Ni:Cr/Si.sub.3 N.sub.4, and the total thickness of the silver remains the same (e.g. 95 .ANG.-105 .ANG.) such that each layer of silver itself is only about 50 .ANG., to make up the total. PA1 a) a layer comprised of Si.sub.3 N.sub.4 and stainless steel, wherein the stainless steel is in an amount of about 0.5%-15% by weight of said layer; PA1 b) a layer of nickel or nichrome; PA1 c) a layer of silver; PA1 d) a layer of nickel or nichrome; and PA1 e) a layer comprised of Si.sub.3 N.sub.4 and stainless steel, wherein the stainless steel is in an amount of about 0.5%-15% by weight of said layer, wherein PA1 when the glass substrate has a thickness of about 2 mm-6 mm, the coated glass substrate has a normal emissivity (E.sub.n) of about 0.06 or less, a hemispherical emissivity (E.sub.h) of about 0.07 or less, a sheet resistance (R.sub.s) of about 5.0 ohms/.sub.sq. or less and has a substantially neutral visible reflected color when viewed from the glass side. PA1 a) a layer of a transparent dielectric material having an index of refraction (n) of about 2.5-2.6 as measured at a wavelength of 550 nanometers; PA1 b) a layer of Si.sub.3 N.sub.4 ; PA1 c) a layer of nichrome (preferably in which at least a portion of the chromium in said nichrome is nitrided); PA1 d) a layer of silver; PA1 e) a layer of nichrome (preferably in which at least a portion of the chromium in said nichrome is nitrided); and PA1 f) a layer of Si.sub.3 N.sub.4 ; PA1 wherein, when the glass substrate has a thickness of about 2 mm-6 mm, the coated glass substrate has a normal emissivity (E.sub.n) of about 0.06 or less, a hemispherical emissivity (E.sub.h) of about 0.07 or less, a sheet resistance (R.sub.s) of about 5.0 ohms/.sub.sq. or less and has a substantially neutral visible reflected color when viewed from the glass side. PA1 R.sub.G Y, about 14 to 20 PA1 a.sub.h, about -2 to +2 PA1 b.sub.h, about 0 to -10 PA1 R.sub.F Y, about 11 to 18 PA1 a.sub.h, about 0 to +4 PA1 b.sub.h, about 0 to -10
In addition to these physical characteristics, the coating system employed must be economical to produce. If it is not, the ultimate product, such as in an IG unit, may become so expensive as to inhibit demand.
It is well-known in the art that these desired characteristics often conflict when attempting to achieve them, and that, therefore, trade-offs often become necessary. For example, achievement of acceptable levels of transmittance or IR (infrared) reflection may have to be at the expense of durability (either chemical or mechanical, or both). In other trade-offs, undesirable colors and mirror-like windows (or doors) become unavoidable. In still further trade-offs, cost of production becomes a significant factor. Such problems create a need in the art for a new sputter-coated layer system which can achieve a better balance among these characteristics.
In U.S. Pat. No. 5,344,718 there are disclosed various excellent sputter-coated layer systems which achieve acceptably low values of emissivity (E), and thus are properly classified as a family of "Low-E" systems (i.e. a family of high IR reflectance coatings). In addition, such coating systems, as a family, generally exhibit durability characteristics which approach or equal those of pyrolytic coatings and thus are quite acceptable. Still further, these coatings, particularly in their preferred embodiments, exhibit high visible transmittance. At the same time they also exhibit a reasonably neutral color, ranging somewhat into the green side of blue which is, however, reasonably masked by the level of visible reflectance achieved to thereby appear substantially neutral. In addition, these visible reflectance characteristics are below 20% and thus also avoid an undesirable mirror-like appearance when viewed from either the inside or outside when used, for example, as a window or door.
The family of layer systems disclosed in U.S. Pat. No. 5,344,718 employs various layers of Si.sub.3 N.sub.4 and nickel or nichrome to sandwich one or more layers of IR reflecting metallic silver between them, in a selected order, thereby to achieve the desired end properties. The entire disclosure of this patent, including the "BACKGROUND" section thereof is incorporated herein by reference.
Generally speaking this prior patent ('718) achieves its unique results by the use of a system comprised of five or more layers wherein from the glass outwardly the system comprises:
When the system consists essentially of these five (5) layers, the following thicknesses are generally employed:
______________________________________ Layer Range (approx.) ______________________________________ a (Si.sub.3 N.sub.4) 400.ANG.-425.ANG. b (Ni or Ni:Cr) 7.ANG. or less c (Ag) 95.ANG.-105.ANG. d (Ni or Ni:Cr) 7.ANG. or less e (Si.sub.3 N.sub.4) 525.ANG.-575.ANG. ______________________________________
When, in this prior patent ('718), more than five layers are employed, such as when two silver layers are employed, the system from the glass outwardly usually includes the following layers:
While such systems as disclosed in this prior '718 patent constitute a significant improvement over then existing prior art systems, particularly those discussed in the "BACKGROUND" section of that patent; nevertheless, there remained room for improvement in the characteristic of "emissivity". For example, in the systems of the '718 patent, normal emissivity (E.sub.n) was generally less than or equal to about 0.12 while hemispherical emissivity (E.sub.h) was generally less than about 0.16. However, in practice, the lower limits realistically or commercially achievable were generally, for E.sub.n about 0.09 and for E.sub.h were about 0.12. Achievable sheet resistances (R.sub.s) in this respect were generally from about 9-10 ohms/.sub.sq.
Inhibiting the achievement of better IR reflection (i.e. decreased "E" values) was the generally held belief that if the thickness of silver were increased to achieve higher IR reflectance (and thus lower "E" values) at least one or more of the following four detrimental effects would occur: (1) there would result a loss of durability; (2) the ultimate product would be too highly reflective, and thus become mirror-like; (3) the color would be driven to an unacceptably high purple or red/blue appearance; and/or (4) visible transmittance would become unacceptably low.
Durability, both mechanical and chemical, is an important factor to achieve in architectural glass generally whether used as a monolithic sheet or, for example, when used in an IG unit. As aforesaid, the handling, assembling and sealing of IG units places a premium on mechanical durability, while the need to edge seal the panes to create an insulating chamber therebetween creates the need for chemical durability due primarily to the nature of the sealant which inevitably contacts the coating. Aesthetically, both mirror-like and purple color qualities may eliminate the marketability of any product exhibiting these characteristics. Loss of visible transmittance while undesirable, does not become truly objectionable until, in a monolithic sheet, it drops below about 70% and in an IG unit it drops below about 63%. However, in certain uses, particularly where low shading coefficients (i.e. less than about 0.6) are desired, transmittance may actually be too high, even though emissivity is reasonably low. Generally speaking, where shading qualities are desired (i.e. to lower air conditioning costs), monolithic visible transmittance should be kept below 75% and preferably below 73%, while in a typical IG unit visible transmittance should be about 65% to 68%.
In partial confirmation of the above beliefs, is the rather complex layer system disclosed in U.S. Pat. No. 5,302,449 as well as its presumed commercial counterpart in IG unit form, known as Cardinal 171 sold by Cardinal IG Company. The layer system as taught in this patent varies the thicknesses and types of materials in the layer stack to achieve certain solar management qualities, as well as employing an overcoat of an oxide of zinc, tin, indium, bismuth, or oxides of their alloys including the oxide of zinc stannate, to achieve abrasion resistance. In addition, the system employs one or two layers of gold, copper or silver to achieve its end results. When two layers of silver are used it is said that the first is between 100 .ANG.-150 .ANG. and preferably about 125 .ANG. in thickness while the second, based thereon, is to be between 125 .ANG.-175 .ANG.. When only one silver layer is employed, it is taught that its thickness is to be about 100 .ANG.-175 .ANG., and preferably 140 .ANG.. Nowhere does this patent disclose the use of nickel or nichrome, nor the use of silicon nitride as an element(s) in the stack arrangement.
In actual commercial practice, the aforesaid Cardinal IG units have been found to achieve quite acceptable solar management properties including acceptable color characteristics and relatively good non-mirror-like visible reflectance (an example is reported hereinbelow for comparison). However, this otherwise quite acceptable system has been found lacking in chemical durability, and, as defined herein, may be said to lack chemical durability since it fails the prescribed boil test. While the precise reason for this is not known, the simple conclusion is that, as has been indicative of the prior art, sacrifices had to be made in at least one desirable characteristic, in order to achieve desirable levels of the others. In addition, due to the nature of the stack and elements used, the system is quite expensive to produce principally due to the number and thickness of the layers required to achieve the desired result.
In the "BACKGROUND" section of the aforesaid '718 patent there is disclosed a further prior art architectural glass layer system which commercially has become known as Super-E III, a product of the Airco Corporation. This system, from the glass outwardly consists of the following layer stack: EQU Si.sub.3 N.sub.4 /Ni:Cr/Ag/Ni:Cr/Si.sub.3 N.sub.4
It has been found in practice that in this Super-E III system the Ni:Cr alloy is 80/20 by weight Ni/Cr, respectively (i.e. nichrome), the two nichrome layers are reported as being 7 .ANG. thick, the Ag layer is specified as being only about 70 .ANG. thick [except that it is stated that the silver may be about 100 .ANG. thick], and the Si.sub.3 N.sub.4 layers are relatively thicker (e.g. 320 .ANG. for the undercoat and about 450 .ANG. for the overcoat). In reality, because of its thinness (i.e. about 70 .ANG.), the silver (Ag) layer has been found, in practice, to actually be rather semi-continuous in nature.
While this coating achieved good "durability" (i.e. the coating was scratch resistant, wear resistant and chemically stable) and thus achieved an important measure of this characteristic as compared to pyrolytic coatings, for glass at about 3 mm thick, E.sub.h is only about 0.20-0.22, and E.sub.n is about 0.14-0.17. Both of these emissivity values are rather high. In addition, sheet resistance (R.sub.s) measures a relatively high 15.8 ohms/.sub.sq. (the more acceptable value being about 10.5 or less). Thus, while both mechanical and chemical durability are found to be quite acceptable and its monolithic sheet visible transmittance was a rather high 76.+-.1%, and while these coatings also proved to be compatible with conventional sealants used in IG units, its ability to handle IR radiation was less than desirable. In addition, its rather high monolithic visible transmittance of 76.+-.1% made such a system rather undesirable when lower shading characteristics were required.
Airco has followed its Super-E III system with what it has designated as its Super-E IV system. This system includes as its layer stack from the glass outwardly the following:
______________________________________ Element Thickness (.ANG.) ______________________________________ TiO.sub.2 Approx. 300 NiCrN.sub.x Approx. 8 Ag Approx. 105 NiCrN.sub.x Approx. 8 Si.sub.3 N.sub.4 Approx. 425 ______________________________________
This system is quite similar in performance to the Super-E III except that visible transmittance is higher (e.g. greater than 80%), emittance is lower (e.g. less than about 0.10) and shading coefficient is significantly higher (e.g. approx. 0.80). While this Super-E IV system employs an undercoat of TiO.sub.2 there is no teaching or recognition when carrying out this system in practice that if the index of refraction of the undercoat of TiO.sub.2 were carefully controlled within certain rather narrow limits, that certain very important improved results could be achieved. Instead, it was left to our invention herein described to discover this unique phenomenon and the unexpected characteristics resulting therefrom.
Another layer system, somewhat similar perhaps to Super-E III and IV, is reported in U.S. Pat. No. 5,377,045. In the systems therein reported, a single silver layer (for example) is sandwiched between two nichrome layers which, in turn, are sandwiched between a lower layer of, for example, TiO.sub.2 or Si.sub.3 N.sub.4 doped with Zr; and an outer layer of Si.sub.3 N.sub.4 or Si.sub.3 N.sub.4 doped with Zr. The use of TiO.sub.2 as an undercoat with a contiguous layer of Si.sub.3 N.sub.4 (doped or undoped) is not disclosed. In addition, the index of refraction of the undercoat layer is specified only generically as "greater than about 2.0 and most preferably between 2.4 and 2.7" [Col. 2, lines 63-64].
The designations of index of refraction disclosed in this patent indicate patentees' adoption of the conventional practice of reference to 550 nanometers as the wavelength, which we also use herein to describe our invention. However, in this patent there is no specified index for TiO.sub.2 and when the patentees specify the use of doped Si.sub.3 N.sub.4 as the undercoat, the index of refraction is said to be between 2.00-2.45, below the limits of index found useful in the practice of our invention. There is, furthermore, no disclosure or recognition in this patent that the index of refraction of TiO.sub.2 may be carefully controlled during the sputtering process by control of the oxygen content in the sputter zone as we do in the practice of our invention. Still further, in the most preferred embodiments of our invention, a significant increase in silver layer thickness is achieved over that reported in this patent. The patent reports a maximum thickness of 150 .ANG., with 90 .ANG.-110 .ANG. being preferred. In contrast, our invention's most preferred range is above 150 .ANG., and preferably about 165 .ANG., enabling the achievement of significantly lower emissivity values.
The layer systems of this patent, in practice, are known to generally be of a purple color, have been found not to be chemically durable as defined by the below-described boil test, are not heat treatable, and have a rather high emissivity. According to this patent, in this respect, special sputtering techniques are said to be needed in order to reduce what is referred to as the "intrinsic stress" in one of the dielectric layers in order to achieve mechanical and chemical desirability according to the tests reported therein used to define these two characteristics.
A significant improvement in the prior art is disclosed in our application Ser. No. 08/356,515 filed Dec. 15, 1994, now U.S. Pat. No. 5,514,476, and entitled LOW-E GLASS COATING SYSTEM AND INSULATING GLASS UNITS MADE THEREFROM. The disclosure of this application is incorporated herein by reference. In this pending application there is disclosed a unique layer system comprised of a silver layer sandwiched between two nichrome layers which, in turn, are sandwiched between a lower and outer layer of Si.sub.3 N.sub.4. By appropriate adjustment of layer thicknesses, the coating systems of that invention achieved advantageously low emissivities (i.e. E.sub.n &lt;0.7, E.sub.h &lt;0.075, R.sub.s &lt;5.5 ohms/.sub.sq.). In addition, the reflectance characteristics (reflectance and extinction) made them quite acceptable (i.e. no mirrorlike appearance) for use in insulating glass units ("IG's"). The transmittance characteristics, as well, were in the appropriate range and the problem of undesirable purple color of past prior art systems was eliminated.
While these layer systems were quite advantageous, it has been found that as one seeks to achieve even lower emissivity values (i.e. reduced infrared transmission, which is a principal object of many layer systems used in architectural and automotive glass), principally through the attempt to thicken the silver layer (the primary IR-reflecting layer), visible transmittance, color, and reflectance characteristics are adversely affected. For example, thickening of the silver layer has been found to severely decrease visible transmittance to below the acceptable 70% level. In addition, the glass side appearance of an article (e.g. IG unit) so coated with too thick a silver layer can often become highly purple and mirrorlike. Thus while the above system described in our aforesaid co-pending application achieved properties theretofore unachieved in combination by the prior art, there was still a need for improvement, if at all possible.
In addition to the layer systems described above, other coatings containing silver and/or Ni:Cr as layers for infrared reflectance and other light management purposes have been reported in the patent and scientific literature. See, for example, the Fabry-Perot filters and other prior art coatings and techniques disclosed in U.S. Pat. Nos. 3,682,528 and 4,799,745 (and the prior art discussed and/or cited therein). See also the dielectric, metal sandwiches created in numerous patents including, for example, U.S. Pat. Nos. 4,179,181; 3,698,946; 3,978,273; 3,901,997; and 3,889,026 just to name a few. While such other coatings have been known or reported, it is believed that prior to our invention, none of these prior art disclosures teach or have achieved the ability to employ the highly productive sputter-coating process and, at the same time, achieve an architectural glass which not only approaches or equals the durability of pyrolytic coatings, but which also achieves excellent solar management qualities as well.
A significant improvement over the previously discussed prior art layer systems is disclosed in our parent, co-pending application Ser. No. 08/552,366 filed Nov. 2, 1995 and entitled NEUTRAL, HIGH PERFORMANCE, DURABLE LOW-E GLASS COATING SYSTEM, INSULATING GLASS UNITS MADE THEREFROM, AND METHOD OF MAKING SAME. The disclosure of this application is incorporated herein by reference.
In this co-pending application there is disclosed a unique sputter-coated layer system which from the glass substrate outwardly includes:
In certain embodiments disclosed in this co-pending application the layer system consists essentially of the above-described five (5) layers. In certain other embodiments so disclosed the layer system includes an optional undercoat of TiO.sub.2. In both such embodiments, the relative thicknesses of the layers may be adjusted so that in certain further embodiments the layer system is "heat treatable" as defined therein, and as similarly defined hereinbelow.
These layer systems when so formed on their appropriate glass substrates provide unique and advantageous coated glass sheets whose solar management, durability, and chemical resistance properties (including reflectance and color properties) make such articles particularly useful in the manufacture of insulating glass units (known as "IG" units in the art). While such layer systems did at times employ an optional undercoat of TiO.sub.2, the use of stainless steel admixed with the layers of Si.sub.3 N.sub.4 was previously felt to be an important aspect of the system as a whole if the desired, maximized results were to be achieved.
The use of stainless steel adds expense and a measure of complexity to the system as a whole and its manufacturing process as well. Thus, if the same advantageous results could be achieved without the use of stainless steel in the Si.sub.3 N.sub.4 layers, a significant advance in the art would be achieved.
In view of the above, it is apparent that there exists a need in the art for a sputter-coated layer system which optimizes rather than unduly sacrifices on a perceived priority basis, the above-described characteristics for coated glass sheets generally, and IG units more particularly, in an economical way. It is a purpose of this invention to fulfill this and other needs in the art which will become more apparent to the skilled artisan once given the following disclosure.